Process for the preparation of pseudo-cyanine dyes



,ployed. plication Serial No. 619,960, filed June 29, 1932 Patented May 6, 1941 PROCESS FOR THE PREPARATION OF PSEUDO-CYANINE DYES Leslie G. S. Brooker, Rochester, N. Y., assignor,

by mesne assignments, to Eastman KodakCompany, Rochester, N. Y.,

Jersey v a corporation of New No Drawing. Original application January 16,

1933, Serial No. 651,870. Divided and this application March 3, 1936, Serial No. 66,860

' 11 Claims. 01. 260-5240) This invention relates to a process for the preparation of cyanine dyes and in particular to a process for the preparation of pseudo-cyanine dyes. ,This application is a division of my cop'endingapplication Serial No. 651,870, filed Jan ;uary16, 1933.

Itis well lrnown that a number of cyanine dye condensaticns are, brought about by using basic media or else by theuse of inorganic alkalies', For instance, 'dyes of what is known as g the pseudo-cyaninetype have been prepared by the actionof causticv potash, in absolute alcoholic so,- lution, on -a'suitable'mixture of quaternary salts of heterocyclic bases. (of. Hamer,J. Chem. Soc. 1928, 206). 4

It is an object of thepr'esent invention to provide a process for effecting pseudo-cyaninedye condensations in the presence of strong organic bases, such as trialkylamines (for example, triethylamine and 'triethanola nine) N-methylpiperidine, and. the like." ,One advantage of this process is that in general the yields of products are much higher than Iwhenemploying older methods, and in some cases products are obtainable which. have heretofore been inaccessible using the older methods. j 1

Distinction should be drawn betweenthels'olateduseof these strong organic bases in small quantities-as; catalysts and their employment in the present instance in molecular equivalent amounts. In the presentcase a perusal of'the examples will show that the strongorganic base is used to bind molecular proportions of acid, and the two types of reaction are, therefore, entirely different. In the present invention the bases are not used as catalysts, but as preferred acid-binding agents.

"The bases which I use, such as n-butylamine,

diethylamine, triethylamin'e, tributylamine, pi-

peridi'ne," N-methylpiperidine, triethanolamine,

andthe like, are of the 'substituted ammonia type and'are recognized as being strong organic'bases. These bases all have a dissociation constant substantially greater than that of pyridine. These bases may also be employed in the form of their salts with weak acids. For instance, guanidine pared with when potassium hydroxide is em-- (See, for instance, myco-pending apnow Unitedstates Patent 2,143,869, dated only from -75%. The corresponding seleniumcontaining dye may besimilarly prepared.

The results are still more striking with 2,1

diethyloxapseudocyanine iodide, a new dye.

This dye, which possesses the following structure,

C-CH I) \N f a 1 Et is obtainable when caustic potash (2 mols.) is allowed to react in absolute ethyl alcoholic solution on a hot mixture of l-methylbenzooxazole ethiodide and 2-:lodoquinoline ethiodide. The yield, however, in that case is small, being around 7%, and thisremains roughly the same when sodium ethylate is used i in place of the caustic potash. However, when triethylamine is used ,the yield of unrecrystallized, but substantially pure dye, is around 67%.'

Of the various methods suggested in my copending application (Serial No. 619,960) for thi -azolopseudoh selen cyanine dyes, those methods in which triethylamine are used are preferred for the reason that the yields are usually better.

Usually triethylamine, tri-n-butylamine, p-diethylaminoethyl alcohol and such tertiary bases,

the preparation of dialkyl- "give very high yields of the pseudo-cyanine dyes,

and these bases are consequently preferred. Guanidine carbonate is quite good too for the preparation of 2,1'-diethylthiopseudocyanlne iodide and of 1,1'-diethylpseudocyanine iodide, the yields being 85% and respectively, under the conditions employed. This reagent, however, is less suitable for preparing 1,2-diethyloxapseudocyanine iodide. Piperidine too, while giving about a 40% yield of 2,1'-diethylthiopseudousing 2-iodo'pyridine 'alkyl iodide and the approyildfofidyelis aboHtB cyanine iodide, gives a small yield of 2,1-diethyloxapseudocyanine iodide or of 1,1 diethylpseudocyanine iodide, but diethylamine gives an 80% yield of this first dye, a 20% yield of the secondyand a 30% yield of the third dye.

The bases should be pure and anhydrous and When tri-n-butylamine is employed (3.7 parts, 2.1 mols.) the conditions being otherwise identical, the yield of dye is 76%. The use of guanidine carbonate (1.9 parts, 1.05 mols.) results in a yield of about 80%.

EXAMPLE 2 the details of preparation of the dyes are fur- I nished in the examples.

A further witness to the improvement the method brought about by the uses of triethylamine and the like in con'densations. of the pseudo-cyanine type is afforded-by the-reaction between 2-iodoquinoline alkyl iodide and alphapicoline alkyl iodide. When caustic potash is employed, a pseudo-cyanine cannot, be isolated (Hamer and Kelly, J. C. 8.1931, 77-8,;seaalso. B. P. 369, 947, page 1, line 32)"b'u't-when t'ri ethylamine is employed, the dye can readily be isolated.

Furthermore, it wasnot found possible (B. P.

369, 947, p. '1, 1. 2-1) to prepare a cyanine dye of the constitution it lt l R n I using potassium "hydroxide but using triet'hyland 'priate quaternary salts of cyclic ammonium bases containing reactive methyl groups.

- The dyes known as'the isocyanines may also conveniently be prepared usin the str'ong "organic bases, and an example appears hereinafter showing how *to prepare the dye 2,'l-di'ethylselenoisocyanine iodide.

7" The following examples serve to illustrate my 2,1'-diethyloa:apseudocyanine iodide in parts of boiling absolute ethyl alcohol with 2.1 part's of triethylamine.

invention, however, it is not intended that these illustrations limit my invention in any manner:

EXAMPLE 1 1 1,1'-diethg Zpseud0cyanine iodide 3 parts of quinaldine ethiodide -(-1 mol.) are heated with 4.1 parts (1 mol.) of finely powdered .2-'iodoquinoline ethiodide in 30 partsof boiling ethyl alcohol under reflux, and 2.1 (2.1 mole, 1. e.

5% excess) parts of triethylamine added down the condenser and the whole well shaken and refluxed for twenty minutes.- The dye forms rapidly, is filtered off when cold, washed with 7 water, followed by allittle alcoholand dried. The

.7 parts which is. about 80% q of the theoretical.

The dye rapidly separates from the boiling solution and refluxing is continued for a further ten minutes. The washed dye weighs 3 parts (67%) and crystallizes from methyl alcohol in orange needles. Triethanolamine (-3.15 parts) gives a yield of about 2 parts 1 EXAMPLE '3 2,1 -diethylthiopseudocyanine iodide 3.5 parts of l-methylbenzothiazole etho-ptoluenesulfonate and 4.1 parts of 2-iodoquinoline ethiodide are treated in 30 parts of boiling ethyl alcohol with 2.1 parts of triethylamine and the mixture refluxed for twenty minutes. The dye separates out and after washing and drying is "obtained in a yield of about A p-Die'thylaminoethyl alcohol (2.5 parts) similarly used results in a yield of 90%. Guanidine carbonate (1.9 parts) gives 'a yield of 86% and 'diethylamine (1.55 parts) gives a yield of 79%.

I EXAMPLE 4 17 met-hyZ-1",2-diethylthiopseudocyanine iodide 3.2parts (1 mol.) of l-ethylbenzothiazole ethiodide (made by condensing equivalent amounts of l-ethylbenzothiazole and ethyl iodide together in the usual way, and recrystalliz'ing the product), 4.1 parts (1 mol.) of 2-iodoquinoline ethiodide and '18 parts of absolute ethyl alcohol are is, refluxed together with "2 parts '(2 mols.) of tri- 7 :Inay be recrystallized from methyl alcohol and is obtained as small scarlet needles which give an orange solution with the solvent.

(1 mol.) of Z-iodoquin'oline ethiodide added, the

whole-brought to boiling at 2.1 2.1 mols.) parts ofg-triethylamine added. The dye rapidly separates but heating is continued for 20 minutes.

On cooling the dye is removed, washed and purified by crystallization from methyl alcohol in which it gives an orange solution. Thedye forms scarlet needles with a blue reflex.

EXAMPLE '6 1,3,3;@ieimmetn zinaopseadecyanine iodide 3 parts (1 mol.) of 2.3,3-trimet'hylindcilenine methiodide and 4.1 parts .(1 mol.) 61J2-iodoquinoline ethiodide were condensed together refluxing the mixture in 20 parts of absolute ethyl aloohol together with 2.1 parts (2.1. mols.) of triethylamine for 25 minutes. The mixture was cooled, the dye precipitated with ether and washed with Water followed by a little acetone. The dye was obtained as a dull brown powder and weighed 3.2 parts (72%). It could be recrystallized from methyl alcohol and formed reddish brown crystals. The yield ofdye obtained is much higher than when potash is used.

EXAMPLE '7 1,1 -dimethyl-5,6-b eneopyrido-2j -cg a7 ine iodide 2,1-diethylthio-2'-pyridocyanine iodide 3.5 parts (1 mol.) of l-methylbenzothiazole etho-p-toluenesulfonate and 3.6 parts (1 mol.) of 2-iodopyridine ethiodide are heated under reflux for 20 minutes with 12 parts of ethyl alcohol and 2.1 parts (2 mols.) of triethylamine. The dye was filtered off when cold. The crude dye contained a sparingly soluble by-product and the dye desired was extracted from this by using a small quantity of hot methyl alcohol. After one more recrystallization, the dye was pure.

EXAMPLE 9 1,1'-dimethyZ-2,2'-pgridocyanine iodide 2.4 parts (1 mol.) of alphapicoline methiodide, 3.5 parts (1 mol.) of 2-iodopyridine methiodide, 16 parts of absolute ethyl alcohol and 2.1 parts (2.1 mols.) of triethylamine are refluxed together. The dye begins to separate in glittering crystals from the boiling reaction mixture after 3 or 4 minutes, and refluxing is continued for 20 minutes. The dye is removed and is purified by washing with acetone followed by water, and is obtained in beautiful light brown plateletswith a. bright pale greenish reflex. It may be recrystallized from methyl alcohol when it is ob: tained in brown granular crystals with a green reflex. The color of the solution is goldenyellow.

EXAMPLE 4,1 '-dimethg/L3-ethylthiazolo-2-pyridocyanine iodide 2.7 parts (1 mol.) of 2,4-dimethylthiazole ethiodide, 3.5 parts (1 mol.) of 2-iodopyridine methiodide, 16 parts of absolute ethyl alcohol are brought to boiling, 2.1 parts (2.1 mols.) of triethylamine added and the whole refluxed for 20 minutes. The dye rapidly separates from the boiling solution as a yellow-orange powder. It is removed, washed with acetone followed by water and may then be recrystallized from methyl alcohol in which it gives a yellow-orange solution. It separates as yellow needles or as orange needles with a bright greenish-yellow reflex, or as a mixture of the two forms.

EXAMPLE 11 3,4,1 -trimethyZselenaeoZo-Z' -pyrido cyanine iodide ZA-dimethylselenazole metho-p-toluenesulfomate (1 mol.) is prepared by heating 1.6 parts (1 mol.) of 2,4-dimethylselenazole with 1.9 parts (1 mol.) of methyl p-toluenesulfonate for several hours at C. The salt soon solidifies and is dissolved in 12 parts of hot absolute ethyl alcohol, 3.5 g. (1 mol.) of 2-iodopyridine methiodide added, the whole boiled, 2.1 parts (2.1 mols.) of triethylamine added and refluxed for 20 minutes. The dye rapidly separates from the boiling solution. It is removed, washed with acetone followed by water and is obtained as a light-brown crystalline powder. It crystallizes from methyl alcohol, in which it gives a deep yellow-orange solution, in glittering minute brown crystals.

If an equivalent amount (1 mol.) of 2,4-dimethyloxazole be used in place of the 2,4-dimethylselenazole, then in the first stage of the synthesis 2',4-dimethyloxazole metho-p-toluenesulfonate is formed, and in the final stage 3,4,1'-trimethyloxazolo-2-pyridocyanine iodide. This compound crystallizes in beautiful yellow needles.

From the foregoing description and numerous examples it will be apparent that the use of a strong organic base, and particularly a strong tertiary organic base, as a condensing agent for the preparation of pseudo-cyanine dyes has a broad and general application. By its use the yields of a large number of pseudo-cyanine dyes is vastly improved and the syntheses of a number of dyes which have heretofore defied preparation is made possible. While many more examples could be given, the foregoing are thought to be suflicient to teach the application of my method to pseudo-cyanine dye condensations in general. It is a striking fact that the simplest pseudocyanine dyes having the general formula are rendered accessible by this method.

While I have described the use of a considerable number of strong organic bases, it will be apparent to those skilled in the art that any strong organic base having similar properties may likewise be employed. In the claims appended hereto, when the term strong organic base is used, it is not intended to include bases such as pyridine and quinoline, but only intended to include those organic bases having a dissociation constant substantially greater than that of pyridine. Furthermore, I employ these strong organic bases in molecular equivalent quantities rather than in traces as catalysts.

More specifically, it will be observed that the strong organic bases which I prefer to employ form a group which, in general, comprises aliphatic bases of the substituted ammonia type known as aliphatic amines. These amines may be primary, secondary or tertiary amines, but are preferably tertiary amines. It is also convenient to employ some of these bases in the form of their salts with weak acids, such as carbonic acid. There'is a great variety of such strong organic bases available, and it is not intended that the concept should be applied too restrictively. For instance, guanidine (in the form of its carbonate) is effective, while at the same time it is not strictly regarded as an aliphatic amine.

All of the dyes herein described have the property to a greater or lesser degree of sensitizing photographic emulsions, such as gelatinosilver-halide emulsions, so as to make these emulsions responsive to light in various portions of the spectrum.

What I claim and desire to secure by Letters Patent of the United States is:

1. In a process for preparing a pseudocyanine dye wherein one molecular proportion of a cyclammonium quaternary salt containing a re active alkyl group in the alpha position is condensed with one molecular proportion of a cyclammonium alkyl quaternary salt selected'from the group consisting of 2-halogeno pyridinium alkyl quaternary salts and 2-halogeno quinolinium alkyl quaternary salts and the elements of acid are eliminated from the condensing cyclammonium alkyl quaternary salts, the step which comprises employing a tertiary organic base having a dissociation constant substantially greater than that of pyridine, in quantity suificient to bind the elements of acid eliminated.

2. In a process for preparing a pseudocyanine dye wherein one molecular proportion of a cyclammonium quaternary salt containing a reactive alkyl group in the alpha position is condensed with one molecular proportion of a cyclammonium alkyl quaternary salt selected from the group consisting of 2-halogeno pyridinium alkyl quaternary salts and 2-halogeno quinolinium alkyl quaternary salts and the elements of acid are eliminated from the condensing cyclammonium alkyl quaternary salts, the step which comprises employing a trialkylamine having a dissociation constant substantially greater than that of pyridine, in quantity sufficient to bind the elements of acid eliminated.

3. In a process for preparing a pseudocyanine dye wherein one molecular proportion of a cyclammonium alkyl quaternary salt containing a reactive methyl group in the alpha position is condensed with one molecular proportion of a cyclammonium alkyl quaternary salt selected from the group consisting of 2-halogenopyridinium alkyl quaternary salts and 2-halogenoquinolinium alkyl quaternary salts and the elements of acid are eliminated from the condensing alkyl quaternary salts, the step which comprises employing a tertiary organic base having a dissociation constant substantially greater than that of pyridine, in quantity sufiicient to bind.

the elements of acid eliminated.

, 4. In a process for preparing a pseudocyanine dye wherein one molecular proportion of a cyclammonium alkyl quaternary salt containing a reactive methyl group in the alpha position is condensed with one molecular proportion of a cyclammonium alkyl quaternary salt selected from the group consisting of 2-halogenopyridinium alkyl quaternary salts and 2-halogenoquinolinium alkyl quaternary salts and the 019-- ments of acid are eliminated from the condensing alkyl quaternary salts, the step which cornprises employing a trialkylamine having a dissociation constant substantially greater than that of pyridine, in quantity sufiicient to bind the elements of acid eliminated.

5. In a process for preparing a pseudocyanine dye wherein one molecular proportion of a cyclammonium alkyl quaternary salt containing a reactive methyl group in the alpha position is condensed with one .molecular proportion of a 2- iodoquinolinium alkyl quaternary salt and the elements of acid are eliminated from the condensing alkyl quaternary salts, the step which comprises employing a tertiary organic base having a dissociation constant substantially greater than that of pyridine, in quantity Sufii? cient to find the elements of acid eliminated.

6. In a process for preparing a pseudocyanine dye wherein one'molecular proportion of a lmethylbenzothiazole alkyl quaternary salt is condensed with one molecular proportion of a 2- iodoquinolinium alkyl quaternary salt and the elements of acid are eliminated from the condensing alkyl quaternary salts, the step which comprises employing a trialkylamine having a dissociation constant substantially greater than that of pyridine, in quantity sufiicient to bind the elements of acid eliminated.

'7. In a process for preparing a pseudocyanine dye wherein one molecular proportion of a lmethylbenzothiazole alkiodide is condensed with one molecular proportion of a 2-iodoquinoline alkiodide and the elements of acid are eliminated from the condensing alkiodides, the step which comprises employing a trialkylamine having a dissociation constant substantially greater than that of pyridine, in quantity sulficient to bind the elements of acid eliminated.

8. In a process for preparing a pseudocyaninc dye wherein one molecular proportion of lmethylbenzothiazole ethiodide is condensed with one molecular proportion of 2-iodoquinoline ethiodide and the elements of acid .are eliminated from the condensing ethiodides, the step which comprises employing a. trialkylamine having a dissociation constant substantially greater than that of pyridine, in quantity suincient to bind the elements of acid eliminated.

9. In a process for preparing a pseudocyanine dye wherein one molecular proportion of 1- methylbenzothiazole ethiodide is condensed with one molecular proportion of '2-iodoquinoline ethiodide and the elements of acid are eliminated from the condensing ethiodides, the step which comprises employing triethylamine to bind the elements of acid eliminated.

10. In a process for preparing a pseudocyanine dye wherein one molecular proportion of a 1- methylbenzoselenazole alkiodide is condensed with one molecular proportion of a 2-iodoquinoline alkiodide and the elements of acid are eliminated from the condensing alkiodides, the step which comprises employing a trialkylamine having a dissociation constant substantially greater than that of pyridine, in quantity sufllcient to bind the elements of acid eliminated.

1 1. In a process for preparing a pseudocyanine dye wherein one molecular proportion of an alpha picoline alkiodide is condensed with one molecular proportion of a 2-iodopyridine alkiodide and the element of acid are eliminated from the condensing alkiodides, the step which coinprises employing a trialkylamine having a dis sociation constant substantially greater than that of pyridine, in quantity sufficient to bind the elements of acid eliminated.

LESLIE G. S. BROOKER. 

